There's a sort of trope that Japanese has no swear words, and instead you insult someone simply by using the wrong level of politeness. As with all these things, it's based on a grain of truth (there are linguistically-encoded formality registers) but it's also really xenophobic and demeaning to essentialise cultures in this way, as it perpetuates racial or national stereotypes of Asians/Japanese people. Plus, you miss out on the actual interesting facts about Japanese honorific speech if you skim the surface like this (you'll have to go somewhere else for those, though, as I am not a Japanese expert). The truth is often more interesting than the factoid and I encourage you to learn more if you didn't know about this!
So probably I didn't even need to bring that trope up apart from I like to share information about languages, but some things I saw lately reminded me that English (and any other language, probably) is also perfectly capable of being highly insulting without using actual insults, and we do it with pragmatics.
First, a tweet from @mralanjohnsmith, his second appearance on this blog in recent times, included this photo and observation:
(Photo shows a cafe's outdoor A-board with things like 'awesome food', 'delicious cakes', 'the best brew', and 'decent staff'.)
Secondly, this one:
Both of these seem to be maligning another establishment but not by directly saying anything bad. They in fact both just say good things about themselves. However, they do it in such a way that we fill in the blanks and infer a whole lot more.
The 'decent staff' cafe has a lot of very enthusiastic words like 'awesome', 'the best'. So among these, 'decent' sounds like fairly low praise, meaning only tolerably good. I had a quick look on Urban Dictionary to see if the kids these days are using it in a more positive sense, and while there are a couple of entries with that sense, most have the 5/10 meaning. It seems strange, then, to put this on your advertising. The cafe could be saying that, if it's honest, its staff are only pretty good, but given that the staff wrote the sign, we might interpret it as more likely that they're comparing themselves to other places. Those other places may have good coffee, but this place has 'the best!' Those other places may have good food, but the food here is 'awesome!'. And by extension, if this place only has 'decent' staff, the other places must have less than decent staff, and the next level down from decent is, well, not good.
The other sign, rather than saying too little, gives us too much information. If you said you serve the best pint for miles around, we interpret this to mean you think you're pretty good, but haven't literally done a taste test and got votes and so on. The non-specific nature of the claim means that it's not verifiable, because it's not meant to be. The pub next door might have something to say about it, but a pub five miles away can safely consider itself out of range of the claim. But as it says 'for 8.5km', which is a specific measurement, it just can't be interpreted as 'a large area' or 'a long way' in the way that a round figure like 'ten miles' could, so we wonder what is precisely 8.5km away. Is it, as the person suggests, that there is some other pub within that range that they're saying is less good? Perhaps the village is 8.5km in size, so it's a way of saying it's the best in the village? or is it, as I think I'd be inclined to think, that 8.5km away is a better pint?